Currently there is increasing interest in catalysts of transition metals having novel structures.
Recently there has been significant interest in Brookhart's ligand which may complex later transition metals to form a catalyst useful in an olefin polymerization process. Such complexes are disclosed for example in World patent application 96/23010 jointly in the names of the University of Carolina at Chapel Hill and E.I. DuPont published Aug. 1, 1996. The Brookhart et al patent application does not teach the complexes of the present invention.
The recent paper (Chem. Comm (1998) p. 849) by Gibson and coworkers at Imperial College UK (and BP) teach complexes having a novel structure that is dissimilar to the complexes of the present invention. It is postulated that the complexes of Gibson et al will have utility in the polymerization of certain monomers such as alpha olefins.
There has been a great deal of work recently by both Exxon in the field of metallocene chemistry and by the Dow Chemical Company in single site constrained geometry complexes. As far as applicant has been able to determine none of the chemistry proposed by either Exxon or Dow contain a carbene structure or a constrained alkyl carbon bonded to a transition metal. There are several patents relating to amidinato complexes of transition metals which are suitable for the polymerization of various olefins. U.S. Pat. No. 5,502,128 issued Mar. 26, 1996, assigned to University of Massachusetts, teaches such complexes may be used to polymerize vinyl aromatic monomers; and U.S. Pat. No. 5,707,913 Issued Jan. 13, 1998, assigned to BASF, teaches such compounds may be used to polymerize olefins. Neither of these patents disclose complexes of the structure of the present invention.
U.S. Pat. No. 5,557,023 issued September, 1996 teaches the use of some complexes of transition metals to oligomerize lower alpha olefins such as ethylene to higher olefins such as hexene and the like. The complexes of the patent do not contain a carbene structure or substituted carbon bonded to the transition metal.
Copending U.S. patent application Ser. No. 09/174,782 filed Oct. 22, 1998 in the name of R. G. Cavell et al discloses the complexes useful in the catalyst of the present invention.
Applicant has been unable to identify any prior art disclosing the catalyst of the present invention for the polymerization of olefins.